Electromagnetic imaging is typically used to inquire into the condition of a particular structure of interest in an object. Structures of interest in a human subject include a particular organ such as the heart, and a particular bone such as the tibia.
Digital tomosynthesis imaging further provides a three dimensional (3-D) image of an object that is reconstructed from a set of two-dimensional (2-D) projection radiograph images. A digital tomosynthesis system includes an X-Ray source and a 2-D X-Ray detector, which is a digital detector. In conventional digital tomosynthesis systems, during data acquisition the X-Ray source is rotated by a gantry on an arc through a limited angular range about a pivot point and a set of projection radiographs of the object are acquired by the detector at discrete locations of the X-Ray source. The detector is maintained at a stationary position as the radiographs are acquired. Imaging of the object from different orientations allows depth information to be incorporated into a final image. This depth information is, of course, unavailable in non-tomosynthesis imaging.
Once the projection radiographs have been obtained, they are then spatially translated with respect to each other and superimposed in such a manner that the images of structures in the tomosynthesis plane overlap exactly. The images of structures outside the tomosynthesis plane do not overlap exactly, resulting in a depth dependent blurring of these structures. By varying the amount of relative translation of the projection radiographs, the location of the tomosynthesis plane can be varied within the object. Each time the tomosynthesis plane is varied, the image data corresponding to the overlapping structures is superimposed and a 2-D image of the structure in the tomosynthesis plane is obtained. Once a complete set of 2-D images of the object has been obtained, a 3-D image of the object is reconstructed from the set of 2-D images.
Computed tomography (CT) is a technique that generally involves subjecting a patient to X-Rays, acquiring digital X-Ray data of a portion of the patient's body, and processing and back-projecting the digital X-Ray data to reconstruct a 3-D image of the object. The image may then be displayed on a display monitor of the CT system.
CT systems typically comprise a gantry, a table, an X-Ray tube, an X-Ray detector array, a computer and a display monitor. The computer sends commands to controllers of the gantry to cause the controllers to rotate the X-Ray tube and/or the detector array at a particular rotational speed to produce relative rotation between the X-Ray tube and the detector array 360° about the patient. The detector array is usually comprised of either a curved array (third generation CT system) of detector elements or a ring (fourth generation CT system) of detector elements. In the case where a ring of detector elements is used, only the X-Ray tube is rotated.
Conventional reconstruction method focus mainly on suppressing the underlying/overlying structures of interest, seldom taking into account the unique characteristics of tomosynthesis projections, especially the spectrum, and optimizing the method to enhance the structures of interest. Early trials on filtered back-projection geometrically transformed the tomosynthesis projections to a form suitable for CT or volumetric computed tomography (VCT) reconstruction. But these methods are known to produce “streaking artifacts.”
Conventional filtered back-projection methods enhance the contrast of structures of interest of certain sizes. Unfortunately, conventional filtered back-projection methods suffer from artifacts generated in the 3-D image that are caused by aliasing and that are also caused by the complexity of optimizing the method for all structures of interest that are present in general X-ray radiography images.
In X-ray radiology, radiologists expect to see medical images that have crisp distinctions. However conventional filtered back-projection methods tend to smooth the image, thus losing many of the finer details in the image.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art to generate a 3-D image from 2-D images of a subject that yield images that have sharp visual distinctions and that also have the details of the 2-D images.